Photographic elements containing surface image and fogged internal image silver halide grains



Apnl 13, 1965 G. w. LUCKEY ETAL 3, 7

PHOTOGRAPHIC ELEMENTS CONTAINING SURFACE IMAGE AND FOGGED INTERNAL IMAGE SILVER HALIDE GRAINS Filed July 20. 1961 EMULS/O/V LA YER Fig. 2

12 A A A A A A A A pulvroaaso EMULSION //fi\. SUPPORT I3 /1-- SUPPORT GEORGE W. LUCKEY JOHN C HOPPE INVENTORS A T TOR/VE Y5 United States Patent 3,178,282 PHDTUGRAPHTC ELEMENTS CGNTAINING SUR- FAQE IMAGE AND FUGGED ETERNAL IMAGE SHAVER HALIDE GRAINS George W. Lucxey and John C. Hoppe, both of Rochester,

N.Y., assig'nors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed July 20, 1961, Ser. No. 125,476 13 Claims. (Cl. 96-68) This invention relates to photographic silver halide emulsions, and more particularly, to photographic elements having increased sensitivity and contrast.

This application is a continuation-in-part application of our earlier application, Serial No. 786,225, filed January 12, 1959, now Patent No. 2,996,382. In this earlier application we described photographic elements comprising a light-sensitive photographic emulsion layer comprising unfogged surface image silver halide grains containing iodide adjacent to fogged internal image silver halide grains. We described that the sensitivity and contrast characteristics of such combinations of surface image emulsions and fogged internal image emulsions are substantially greater than those obtainable from either type of emulsion used alone. However, at least a small amount of an iodide such as silver bromoiodide or silver chlorobromoiodide was utilized in the emulsions described in our aforementioned application, it being described that such iodides were useful in imparting the improved properties to the emulsions.

It is an object of this invention to provide novel photographic elements having improved sensitivity.

It is another object of this invention to provide novel photographic elements having increased contrast.

It is another object of this invention to provide novel photographic silver halide emulsions free of silver iodide.

It is another object of this invention to provide a new process for developing photographic silver halide emulsions free of silver iodide.

t is still another object of this invention to provide novel emulsions that are useful in reversal processes.

These and other objects of the invention are attained by means of this invention as described more fully hereinafter with reference to certain preferred embodiments thereof.

We have found that photographic elements having coated thereon blends or mixtures of surface latent image silver halide emulsions and fogged internal latent image silver halide emulsions, or these two types of emulsions coated in contiguous layers on photographic elements,

can be utilized to produce such improved properties as increased sensitivity and contrast in the absence of iodide in the emulsion. We have found that such useful properties can be obtained with the emulsions of the invention by utilizing developer compositions having certain specified rates of silver halide solubility.

The photographic elements of our invention are illustrated by the accompanying drawings. P16. 1 illustrates a fragmentary sectional view 'of a photographic element comprising support and photographic silver halide emulsion layer 11 which includes unfogged surface image grains 12 and fogged internal image grains 13. In FIG. 2 there is illustrated a fragmentary section view of a photographic element comprising support 10, photographic silver halide emulsion layer 14 which includes fog ed internal image grains 13 and photographic silver halide emulsion layer 15 which includes unfogged surface image grains 12. In FIG. 3 there is illustrated a fragmentary sectional view of a photographic element comprising support 1%, photographic silver halide emulsion layer 16 which includes unfogged surface image 3,178,282 Patented Apr. 13, 1965 grains 12 and fogged internal image grains 13, and layer 17 which includes fogged internal image grains 13.

The surface image emulsions useful in our invention comprise those which, when measured according to normal photographic testing techniques by coating a test portion of the emulsion on a transparent support, exposing the test portion to a light intensity scale for a fixed time between 0.01 and 1 second and development for 6 minutes at 68 F. in Developer A as hereinafter defined, have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of the same emulsion which has been exposed in the same way, bleached 5 minutes in aqueous 0.3 percent potassium ferricyanide solution at 65 F., and developed for 5 minutes at 65 F. in Developer B as hereinafter defined. Developer A is the usual type of surface image developer and Developer B is an internal developer having high silver halide solvent activity. The degree of internal sensitivity of the surface image emulsions is not particularly critical. The surface image emulsion can have relatively little internal sensitivity or it may have a fair amount of internal sensitivity, but preferably not greater than the surface activity. Suitable surface image silver halide emulsions (silver bromide, silver chloride and silver chlorobromide) can be prepared by the method described by Trivelli and Smith in The Photographic Journal, Volume LXXX, July 1940 (pages 285-288). The surface image emulsions can have high or low contrast, and useful effects have been obtained with both types of emulsions. The surface image emulsions useful in our invention can also be characterized as having a D max. greater than about 0.50 when the emulsion is coated at a coverage of about 5 40 mg. of silver per square foot, exposed to a stepwedge and processed for 12 minutes in Developer C as hereinafter defined. The surface image emulsions of the invention contain no silver iodide.

The internal image emulsion useful according to our invention is one which, when measured according to normal photographic techniques in its unfogged stage by coating a test portion of the emulsion on a transparent support, exposing to a light intensity scale having a fixed time between 0.01 and 1 second, bleach ing 5 minutes in a 0.3% potassium ferricyanide solution at 65 F. and developing for about 5 minutes at 65 F. in Developer B, has a sensitivity, measured at a density of 0.1 above fog, appreciably greater (e.g., at least 1.4 log E greater) than the sensitivity of an identical test portion which has been exposed in the same way and developed for 6 minutes at 68 F. in Developer A. Several suitable emulsions of this type are described in Davey and Knott US. Patent 2,592,250, issued April 8, 1952. Silver chloride, silver bromide and silver chlorobromide emulsions of the internal latent image type can be used in our invention. The internal image emulsions of the invention contain no silver iodide.

The internal image emulsions useful in our invention must be fogged, partly or completely, before use. The fogging should be suificient to give a density of at least 0.50 when one mole (AgX) of the fogged emulsion is coated in a blend with 3 moles of surface image emulsion at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in Developer B above. The surface D max. of the unfogged internal image emulsions should be less than about 0.30 when the emulsions are exposed to D max. and processed for 8 minutes in Developer C, as identified below.

The fogging of the internal image emulsions useful in our invention can be effected by merely exposing the emulsions to light; or other methods, such as chemical fogging methods, can be used. The emulsions having high internal fog but low surface sensitivity can be prepared by fogging an emulsion having both internal and surface sensitivity and then bleaching the surface image with a solution of potassium ferricyanide. Another means of obtaining our fogged internal image emulsions is by exposure of nonfogged internal image emulsions to high energy radiation, such as X-rays.

The ratio of the surface latent image emulsion to the fogged internal image emulsion can be varied, depending upon the types of emulsions used, the contrast of the emulsions and other known variables. In general, quite useful results are obtained in those cases where the molar ratio of the surface image emulsion is at least equal to or greater than that of the fogged internal image emulsion. Useful results can be obtained even where the molar ratio, as explained above, was 10:1. Where the molar percent of the fogged internal image emulsion exceeds that of the surface image emulsion, such as a 1:3 ratio of surface to fogged internal image emulsion, there is some loss of speed, although the contrast of the combination is considerably greater than that of the surface latent image emulsion. Accordingly, useful results have been obtained where the molar ratio of surface to fogged internal image emulsion varies from about 10:1 to 1:3. These useful effects are illustrated in the examples given below.

The following developing solutions were referred to hereinabove.

Grams A. N-methyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5 Water to make 1 liter.

B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide Sodium thiosulfate 10 Water to make 1 liter.

C. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite, desiccated Hydroquinone 2.5 Sodium metaborate 10 Potassium bromide 0.5

Water to make 1 liter.

The photographic layers used in our invention can comprise blends or mixtures of surface image emulsions and fogged internal image emulsions, or these two types of emulsions can be coated in contiguous layers of the photographic element. In coating the two types of emulsions in separate layers, either emulsion can be coated on top, since the fogged internal image emulsions have sufficient transparency to enable the surface image emulsion to be placed closest to the support and still receive sufiicient transmitted radiation through the fogged internal latent image emulsions for exposure. Exposure of the emulsion closest to the support can also be made through the support where this is transparent. However, for convenience of processing, the surface image emulsion is preferably coated over the fogged internal emulsion. Alternatively, the two types of emulsions can be mixed as a blend and coated over an emulsion layer comprising a fogged internal image emulsion, which may be identical to or different from the fogged internal image emulsion in the blend.

The photographic silver halide emulsions of the invention require for development developers that are characterized as having low solvent action for silver halides and a high rate of solution for silver halides. Suitable developers are aqueous developer compositions in which: 1) silver bromide has a rate of solubility greater than that in a solution containing 5 grams of potassium bromide and 20 grams of sodium sulfite per liter. of developer composition at 68 F., and, (2) silver bromide has a rate of solubility less than that in a solution containing grams of potassium bromide and .90 grams of sodium sulfite per liter of developer composition at 68 F., the second mentioned solution defining the upper concentration level of the potassium bromide and sodium sulfite being free of other addenda which increase the rate of solution of silver bromide and free of photographic antifoggant addenda. Illustrative suitable developer compositions for the emulsions of the invention contain 5 to 35 grams of alkali metal bromide (e.g., sodium bromide or potassium bromide) per liter of developer composition and 20 to 90 grams of alkali metal sulfite (e.g., sodium sulfite or potassium sulfite) per liter of developer composition. Photographic elements having coated thereon blends or mixtures of surface image silver halide emulsions and fogged internal image silver halide emulsions such as illustrated by FIG. 1 of the drawings are preferably processed with developer compositions containing 20 to 30 grams of the alkali metal sulfite per liter of developer composition, and photographic elements having coated thereon discrete and contiguous layers of a surface image silver halide emulsion and a fogged internal image silver halide emulsion such as illustrated by FIG. 2 of the drawings are preferably processed with developer compositions containing to grams of the alkali metal sulfite per liter of developer composition.

The developers utilized to process the subject emulsions have low solvent action but a high rate of solution for silver halides. This rate of solvent action is defined above in terms of rate of solubility of silver bromide in certain concentrations of potassium bromide and sodium sulfite free of other addenda which would increase the rate of solution of silver bromide and free of antifoggants. However, it is to be understood that developers not containing potassium bromide and sodium sulfite, or containing potassium bromide and sodium sulfite in concentrations other than the reference concentrations, or developers containing antifoggants, can be suitably utilized in our invention. For example, other developer addenda such as thiosulfates, quaternary salts, thiocyanates, ammonia and the like known developer addenda can be used which substantially modify the rate of solution of silver halides, reference being made to Photographic Science and Technique, Series II, volume 2, No. 4, pages 135443, and to Journal of Physical Chemistry, volume 6-2, pages 1189-1194 (1958). Likewise, well-known antifoggants, stabilizers or development restrainers can be present during the development of the subject emulsion if desired. Such antifoggants are'well-known in the art, reference being made to Mees, The Theory of the Photographic Process, 1954, pages 678679.

Developer compositions which cause general development of the fogged internal latent image grains on develop ment of a latent image on the surface image grains of the emulsions of the invention are to be avoided as such would darken the entire emulsion and no silver image could be produced. Developer compositions for blends of the subject surface image silver halide grains and fogged internal image silver halide grains should not contain addenda (e.g., potassium iodide) which cause cracking or Keimbiosslegung (H. Luppo-Cramer, Die Grundlagen der Photographischen Negativverfahre Eders Handbuch, II, part i, Wilhelm Knapp Verlag, l-lalle (Saale) (1927), pp. 220-222 and chapter 11) of the fogged internal image silver halide grains unless the concentration of such addenda are maintained at very low levels. However, in processing double-coated emulsion such as illustrated by FIG. 2 of the drawings wherein the surface image silver halide grains are coated on top of the fogged internal image silver halide grains beneficial results are obtained by adding such cracking addenda as the undeveloped emulsion layer having surface image silver halide grains acts as a resist and prevents penetration of the cracking addenda to the under-coated emulsion layer having fogged internal image silver halide grains while permitting penetration of the cracking addenda in the developing or latent image areas of the emulsion layer having surface image silver halide grains.

We have found that fog which may accompany forced or prolonged development of the emulsions of the invention can be removed by a brief bleach treatment before fixing. A typical bleach bath consists of grams potassium ferricyanide and 20 grams of potassium bromide in a liter of water.

The photographic silver halide emulsions of the inventions can be utilized in reversal processes to produce direct positives. In conventional reversal processing the exposed silver halide grains are developed and the resulting silver image bleached with such agents as potassium bichromate and cleared with such agents as sodium sulfite leaving unexposed and undeveloped silver halide. This remaining silver halide is then generally fogged with solutions of such fogging agents as sodium stannite, alkaline hydrosulfite, fogging developer-s containing hydrazine, and the like well-known fogging agents. The resulting logged silver halide is then developed to produce a positive image. However, t e emulsions of the invention can be utilized in reversal processes without the necessity of a fogging step. In reversal processing with the emulsions of the invention the emulsion is first developed in a developer as described hereinabove and then bleached and cleared in the usual manner. Then, without the necessity of a fogging step, the emulsion is developed in a developer containing a cracking agent as described above and which causes general development of the pre-fogged internal image silver halide grains. In a similar manner the emulsions of the invention can be utilized in reversal color processes without the necessity of the conventional light fogging step. The emulsions described in our aforementioned earlier application can also be suitably utilized in such reversal processes wherein a fogging step is not necessary.

A wide variety of conventional photographic silver halide emulsion addenda can be added to the emulsions of the invention as described hereinafter. However, such addenda are usually just added to the surface image emu] sion portion of the subject invention.

The emulsions of our invention can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, and Sheppard et a1. U.S. Patent 1,623,499, issued April 5, 1927, and Sheppard and Brigham U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948, and as antifoggants in higher amounts, as described in Trivelli and Smith US. Patents 2,566,245, issued August 28, 1951, and 2,566,263, issued August 28, 1951.

The emulsions can also be chemically sensitized with gold salts as described in Waller et al., U.S. Patent 2,399,083, issued April 23, 1946, or stabilized with gold salts as described in Damschroder U.S. Patent 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S. Patent 2,597,915, issued May 27, 1952. Suitable compounds are potassium chloroaurite, aurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones U.S. Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Patent 2,521,925, issued September 12, 1950), or bis(B-aminoethyl)sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine and merocyanine dyes as indicated above, such as those described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854, issued January 9, 1934; White U.S. Patent 1,990,507, issued February 12, 1935; Brooker and White U.S. Patents 2,112,140, issued March 22, 1938; 2165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950; and 2,739,964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950 and 2,519,001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; Heseltine U.S. Patent 2,734,900, issued February 14, 1956; Van Lare U.S. Patent 2,739,149, issued March 20, 1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.

The emulsions can also be stabilized with the mercury compounds of Allen, Byers, and Murray U.S. Patent 2,728,663, issued December 27, 1955; Carroll and Murray U.S. Patent 2,728,664, issued December 27, 1955; and Leubner and Murray U.S. Patent 2,728,665, issued December 27, 1955; the triazoles of Heimbach and Kelly U.S. Patent 2,444,608, issued July 6, 1948; the azaindenes of Heimbach and Kelly U.S. Patents 2,444,605 and 2,444,606, issued July 6, 1948; Heimbach U.S. Patents 2,444,607, issued July 6, 1948, and 2,450,397, issued September 28, 1948; Heimbach and Clark U.S. Patent 2,444,609, issued July 6, 1948; Allen and Reynolds U.S. Patents 2,713,541, issued July 19, 1955 and 2,743,181, issued April 24, 1956; Carroll and Beach U.S. Patent 2,716,062, issued August 23, 1955; Allen and Beilfuss U.S. Patent 2,735,769, issued February 21, 1956; Reynolds and Sagal U.S. Patent 2,756,147, issued July 24, 1956; Allen and Sagura U.S. Patent 2,772,164, issued November 27, 1956, and those disclosed by Birr in Z. wiss. Phot., vol. 47, 1952, pages 2-28; the quaternary benzothiazolium compounds of Brooker and Stand U.S. Patent 2,131,038, issued September 27, 1938; the disulfides of Kodak Belgian Patent 569,317, granted July 31, 1958; and the zinc and cadmium salts of Jones U.S. patent application Serial No. 493,047, filed March '8, 1955.

The emulsions can also contain speed-increasing compounds of the quaternary ammonium type of Carroll U.S. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; and the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955.

The emulsions can contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alkane such as 1,5-pentane diol as described in Milton and Murray U.S. Patent 2,960,404, issued November 15, 1960; an ester of an ethylene bis-glycolic acid such as ethylene bis(methyl glycolate) as described in Milton US. Patent 2,904,434, issued September 15, 1959; bis-(ethoxy diethylene glycol) succinate as described in Gray U.S. Patent 2,940,854, issued June 14, 1960; or a polymeric hydrosol as results from the emulsion polymerization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrene-type compound as described in Tong U.S. Patent 2,852,386, issued June 14, 1960. The plasticizer can be added to the emulsion before or after the addition of a sensitizing dye, if used.

The emulsions can be hardened with any suitable hardener for gelatin such as formaldehyde; a halogensubstituted aliphatic acid such as mucobromic acid as described in White US. Patent 2,080,019, issued May 11, 1937; a compound having a plurality of acid anhydride groups such as 7,8-diphenylbicyclo(2,2,2)-octene-2,3,5,6- tetracarboxylic dianhydride, or a dicarboxylic or a disulfonic acid chloride such as terephthaloyl chloride or naphthalene 1,5-disulfonyl chloride as described in Allen and Carroll U.S. Patents 2,725,294 and 2,725,295, both issued November 29, 1955; a cyclic 1,2-diketone such as cyclopentane-1,2-dione as described in Allen and Byers US. Patent 2,725,305 issued November 29, 1955; a biscster of methane-sulfonic acid such as 1,2-di-(methanesulfonoxy)- ethane as described in Allen and Laakso U.S. Patent 2,726,162, issued December 6, 1955; 1,3-dihydroxymethylbenzimidazol-2-one as described in July, Knott and Pollak US. Patent 2,732,316, issued January 24, 1956; a dialdehyde or a sodium bisulfite derivative thereof, the aldehyde g1 cups of which are separated by 2-3 carbon atoms, such as fl-methyl glutaraldehyde bis-sodium bisulfite; a bisaziridine carboxamide such as trimethylene bis(1-aziridine carboxamide) as described in Allen and Webster US. Patent 2,950,197, issued August 23, 1960; or 2,3-dihydroxy dioxane as described in Jetfreys US. Patent 2,870,013, issued January 20, 1959.

The emulsions can contain a coating aid such as saponin; a lauryl or oleoyl monoether of polyethylene glycol as described in Knox and Davis US. Patent 2,831,766, issued April 22, 1958; a salt of a sulfated and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent 2,719,087, issued September 27, 1955; an acylated alkyl taurine such as the sodium salt of N-oleoyl-N-methyl taurine as described in Knox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a'dianhydride of tetracarboxybutane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tetracarboxybutane as described in Knox, Stenberg and Wilson U.S. Patent 2,843,427, issued July 15, 1958; a water-soluble maleopimarate or a mixture of a watersoluble maleopimarate and a substituted glutamate salt as described in Knox and Fowler US. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodium N-(carbo-p-tert. octylpnenoxypen'taethoxy)glutamate; or a sulfosuccinnamate such a tetras-odium N-(1,2-dicarboxyethyl)-N- octadecyl sulfosuccinamate or N-lauryl disodium sulfosuccinamate.

In the preparation of the silver halide dispersions employed for preparing the subject silver halide emulsions,

there can be employed as the dispersing agent for the silver halide gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which can be used are polyvinyl alcohol, or a hydrolyzed polyvinyl acetate as described in Lowe US. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 19-26% as described in US. Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy US. Patent 2,322,085, issued June 15, 1943; a polyacrylamide having a combined acrylamide content of -60% and a specific viscosity of 0.251.5 on an imidized polyacrylamide of like acrylamide content and viscosity as described in Lowe, Minsk and Kenyon US. Patent 2,541,474, issued February 13, 1951; zein as described in Lowe US. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith US. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copoiymer as described in Unruh, Smith and Priest US. Patent 2,808,331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in US. application Serial No. 527,872 of Illingsworth, Dann and Gates, filed August 11, 1954. If desired, compatible mixtures of two or more of these colloids can be employed for dispersing the silver halide in its preparation. Combinations of these antifoggants, sensitizers, hardeners, etc., can be used.

The addenda described above for use in conjunction with our emulsions can be employed in emulsions designed for X-ray photography, or in non-optically sensitizcd emulsions, or orthochromatic, panchromatic or infrared sensitized emulsions. They can be added before or after sensitizing dyes are added. These addenda can also be used in emulsions designed for color photography, for example, emulsions containing color-forming compounds or couplers, or emulsions to be developed in solutions containing such couplers, or emulsions of the mixed-packet type, such as described in Godowsky US. Patent 2,698,794, issued January 4, 1955, etc.

As indicated above, the emulsions having a high degree of internal sensitivity can be prefogged by means of light. It has been found in certain instances-that a mottlelike effect is produced, due to a variation in the graininess pattern over an area of larger scale than the normal graininess pattern. The extent of the irregular mottle pattern of the image can be limited by superimposing a regular screen pattern, such as a gravure tint or a half ton-e contact screen or the type used in the graphic arts industry, on the internally sensitive emulsion layer during the fogging operation with light. The surface sensitive emulsion can then be coated over the fogged internally sensitive emulsion.

Ithas been found that the screen pattern can be made fine enough (e.g., lines per inch) so that the pattern is barely noticeable and the overall visual impression of the image is not adversely affected. Some loss in speed and contrast may sometimes result from such a proce dure, although the improvement in image quality more than offsets this insignificant loss of speed and contrast.

The supports useful in our photographic elements comprise conventional supports, such as paper, cellulose ester film, polyvinyl resin film, polystyrene film, polyester film, etc., as well as non-flexible supports, such as glass.

The invention is further illustrated by the following examples of preferred embodiments thereof.

EXAMPLE 1 A gelatino-silver bromide emulsion (Emulsion No. 1 below) having high surface sensitivity and low internal sensitivity was prepared essentially as described by Yutzy et al. in US. Patent 2,614,928, issued October 21, 1952. A second gelatino-silver bromide emulsion (Emulsion No. 2 below) having high internal sensitivity was prepared essentially as described by Davey et al. in US. Patent 2,592,250, issued April 8, 1952. A portion of Emulsion No. 2 was fogged with light and this fogged emulsion is designated as Emulsion No. 3 below. Samples of Emulsion No. 1 were coated on cellulose acetate at a coverage of 405 mg. of silver per square foot. Blends of about 3 parts by weight of Emulsion No. 1 and 1 part by weight of Emulsion No. 2, and an emulsion blend of the invention, namely, a blend of 3 parts by weight of Emulsion No. 1 and 1 part by weight of Emulsion No. 3, were coated on cellulose acetate film supports at a coverage of 540 mg. of silver per square foot. The prepared film samples were exposed in an Eastman Process Sensitometer with a Kodak Wratten Filter No. 47B and a neutral density of 1.4 in the filter holder. The current through the lamp in the sensitom ter was 0.793 ampere and only one flash was used. The exposed samples were then developed and fixed. Reference is made to Henn and Hughes, Phot. Sci. and Eng, 2, 81 (1958), for a description of the processing device utilized. The developments of the exposed samples were effected at 8, 12 and 20 minute intervals at 20 C. in a developer having the following formulation:

Water to make 1 liter and sodium hydroxide to pH of 9.2.

The results of the sensitometric tests are summarized by the data set out in Table A below. In Table A the relative speeds indicated are a function of the exposure necessary to give a density of 0.3 above background fog and expressed as a reciprocal relation to exposure, the

no tablet density was determined with no step tablet in the light beam of the sensitometer.

Table A 8 MINUTE DEVELOPMENT Emulsion No. Relative Gamma Fog Density, speed no tablet 12 MINUTE DEVELOPMENT MINUTE DEVELOPMENT As can be observed from the data set out in Table A, the surface image emulsion (Emulsion No. 1) is substantially improved with respect to speed and contrast (gamma) when admixed with the fogged internal image emul- EXAMPLE 2 A gelatino-silver bromide emulsion (Emulsion No. 4 below) having high surface sensitivity and low internal sensitivity was prepared essentially by the method described in US. Patent 2,614,928. A gelatino-silver chlorobromide emulsion (Emulsion No. 5 below) having high internal sensitivity was prepared essentially as described in US. Patent 2,592,250. A portion of Emulsion No. 5 was fogged with light and this fogged emulsion is designated Emulsion No. 6. Samples of Emulsion No. 4 were coated on cellulose acetate at a coverage of 540 mg. of silver per square foot. Blends of Emulsion No. 4 and Emulsion No. 5, and an emulsion blend of the invention, namely, a blend of Emulsion No. 4 and Emulsion No. 6, were coated on cellulose acetate film supports at a coverage of 720 mg. of silver per square foot, the coverage of the internal image emulsions in these blends being 180 mg. of silver per square foot. Test samples of the coated films were exposed to a watt sunlamp for ,5 second and processed as described in Example 1 except that the developer employed had 4 grams of hydroquinone instead of 40 grams per liter of developer. The results of the test are summarized by the data set out in Table B below. The data in Table B are in the same units as the data in Table A.

Table B 12 MINUTE DEVELOPMENT Emulsion N0. Relative Gamma Fog Density, speed no tablet 20 MINUTE DEVELOPMENT The data in Table B further illustrates the improved speed and contrast resulting when a surface image emulsion (Emulsion No. 4) is blended with a fogged internal image emulsion (Emulsion No. 6). The unfogged internal image emulsion (Emulsion No. 5) did not demonstrate these same properties when blended with the surface image emulsion. Here again the improved results were obtained in the absence of iodide in the emulsion by utilizing the described developer.

EXAMPLE 3 A gelatino-silver chloride emulsion having high surface sensitivity and low internal sensitivity was prepared essentially by the method described in US. Patent 2,614,928. Also a gelatino-chlorobromide emulsion (53% chloride and 47% romide) having high internal sensitivity was prepared essentially as described in US. Patent 2,592,250. A portion of the internal image emulsion was fogged with light. These prepared emulsions were coated on cellulose acetate film in blends and as juxtapositioned layers as described in Table C below and exposed in an Eastman Process Sensitometer with a Kodak Wratten Filter No. 18A. The color temperature of the exposure lamp was 2850 K. After exposure, the coatings were developed in a variety of developers for varying times at 20 C. in a process as described in J. Phot. Sci. and Engr., 2, 81 (1958). After development, the coatings were fixed, washed and dried in the conventional manner. Table C below summarizes the various coatings subjected to the sensitometric tests.

Table C Silver coverage, mgJft.

Type of coating 1 1 The compositions of five difierent developers utilized to develop the above-described emulsion coatings are de scribed in Table D below.

In Table D, the pH of the various developer-s was adjusted to with sodium hydroxide, and the numbers indicate grams of developer component per liter of water. The sensitometric data when the coatings described in Table C are developed in the developers described in Table D are summarized in Tables E to H below. In Tables E to H, the speeds indicated are a function of the exposure necessary to give a density of 1.0 above background fog and expressed as a reciprocal relation to ex- Gamma was taken between a density of 1.0 and 12 of the invention can be obtained when the surface image emulsion is coated directly over the fogged internal image emulsion (Coating No. IV), as well as by blending these two types of emulsions.

Table G Coating No. Developer Devel. Relative Density,

time, speed 7 no tablet Fog Coating No. TV is a photographic element of the invention wherein the surface image emulsion is coated over a fogged internal image emulsion. As demonstrated by the data set out in Table G, such photographic elements have increased speeds and density. The data in Table G further illustrates that small amounts-of an alkali metal iodide in the developer can be suitably utilized in devel- P oping double coated photographic elements of the inven- 2.0. tron. Developer P has a slightly higher concentration of alkali metal iodide than Developer 0, this increase in Table E iodide increased the rate of development.

Coating Devel. Relative Density, Table H No. Developer time, speed 7 no tablet Fog min.

10 47 3. 0 3. 1 0. 12 Devel. Relative Density, 12 62 3.0 3.5 0.15 Coating No. Dev p t me, speed 1 no tablet Fog 15 80 3.2 4 0. 24 min. 20 110 1.7 4 0.81 20 is 2.0 1.7 0.13 30 19 2.1 1.8 0. 19 12 2. 7 4 0. 31 e0 16 2. 0 1. 8 0. 45 20 70 3. 7 4 0. 57 20 41 1.9 2.6 0.22 12 22 3.9 2.7 0.16 30 42 1. s 2. 7 0. 30 20 33 s. 4 4 0. 22 so 25 1. 4 2. 7 0. e5 30 45 4. 6 4 0. 30 12 4 30 7 1.9 3.3 0.38 e0 1.6 3.4 0.58 30 58 2.5 3.5 0.28 60 58 1.0 3.6 0. 51 g 5 3.2 2.4 0.20 L 2.6 0.32 A can be ooserved from the data Set ou n Table 2 r3 Coating No. I of the invention, which was a blend of the surface image emulsion and the fogged internal image emulsion, exhibited substantially improved speed and contrast over the surface image emulsion alone or a blend of the surface image and the uniogged internal image emulsion.

The data in Table F illustrates that the improved results The data in Table H illustnates the use of a small amount of antifoggant (Developer Q contains 0.0025 g./liter of l-phenyl-5-mercaptotetrazole) in processing photographic elements of the invention (Coating Nos. I and IV).

EXAMPLE 4 A gelatino-silver chlorobromide emulsion (60% bromide and 40% chloride) having high surface sensitivity and low internal sensitivity Was prepared essentially by the method described in U.S. Patent 2,614,928. Also a gelatino-chlorobromide emulsion (53% chloride and 47% bromide) having high internal sensitivity was prepared essentially as described in U.S. Patent 2,592,250. A portion of the internal image emulsion was fogged with light. The prepared emulsions Were coated on cellulose acetate film in blends and as juxtapositioned layers, and thereafter tested with a sensitorneter by the method described in Example 3 with three developers at varying Table 1 Silver coverage, mg. lit.

Coating N0. designated in Type of coating Tables K to M Surface image emulsion alone 1 part unfogged internal image emulsion blended with 3 parts surface image emulsion.

1 part logged internal image emulsion blended with 3 parts surface image emulsion.

2 parts surface image emulsion coated over 1 part unfogged internal image emulsion.

2 parts surface image emulsion coated over 1 part iogged internal image emulsion.

The compositions of the three developers utilized to develop the above-described emulsion coatings are described in Table I below.

Table 1 Developer designation in Tables K to M R S T 1-phenyl-3-pyrazolidone 1 1 1 Sodium sulfite. desiccated- 20 60 6O Hydroquinone 1O Sodium metaborate 30 30 40 Potassium bromide 10 10 10 Sodium sulfate. 47 1. 7 0 Potassium sulfate 18 18 0 l-phenyl-fi-mercaptotettazole 0 0 0. 0025 In Table I, the pH of the various developers was adjusted to 10 with sodium hydroxide, and the numbers indicate grams of developer component per liter of water. The sensitometric data when the coatings described in Table I are developed in the developers described in Table I are summarized in Tables K to M below. In Tables K to M the relative speeds indicated are a function of the exposure necessary to give a density of 1.0 above background fog and expressed as a. reciprocal relation to expo- Coating No. IX is a photographic element of the invention wherein a fogged internal image emulsion is blended with a surface image emulsion, and its improved speed and contrast is illustrated by the data set out in Table K above.

Table L Coating Devel. Relative Density,

No. Developer time, speed 7 no tablet Fog min.

8 38 1. 6 2. 2 0. 24 10 49 1.8 2. 6 0. 30 12 60 2. 3 3. 5 0. 36 23 -0. 8 l. 5 0. 25 22 -0. 8 1.6 0. 38 20 47 l. 2 2. l 0. 32 30 33 1. 1 2.2 0. 54

Coating No. X1 is a photographic element of the invention having a surface image emulsion coated over a 14 fogged internal image emulsion, the data in Table L pointing up the improved results of such photographic elements.

Table M Coating Devel. Relative Density,

0. Developer time, speed 7 no tablet Fog min.

The present invention thus provides new and useful photographic elements and emulsions.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic element comprising a support and at least one light-sentitive photographic silver halide emulsion layer, said silver halide being selected from the group consisting of silver chloride, silver bromide and silver chlorobromide, said photographic element having unfogged surface image silver halide grains (I) adjacent to fogged internal image silver halide grains (II), said unfogged surface image silver halide grains (I) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (1) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-aminophenol sulfate 2.0 Sodium suliite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter,

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A),

said fogged internal latent image silver halide grains (II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (I) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B).

2. A photographic element comprising a support and a first discrete silver halide emulsion layer containing unfogged surface image silver halide grains (I) and contiguous to said first discrete silver halide emulsion layer a second discrete silver halide emulsion layer containing fogged internal image silver halide grains (II), said silver halide being selected from the group consisting of silver chloride, silver bromide and silver chlorobromide, said unfogged surface image silver halide grains (I) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Grams A. N-methyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter,

said fogged internal image silver halide grains (11) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A), said fogged internal latent image silver halide grains (11) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (I) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B).

3. A photographic element comprising a support and an emulsion blend containing unfogged surface image silver halide grains (1) and fogged internal image silver halide grains (11), said silver halide being selected from the group consisting of silver chloride, silver bromide and s-ilver chlorobromide, said unfogged surface image silver halide grains (I) :being such as to cause a test portion thereof, when coated as a photographic silver halide emul- ,sion on a transparent support and upon exposure to a 156 light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Grams A. N-methyl-p-aminophenol 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfi-te 1.5

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (1) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-arninophenol sulfate 2.0 Sodium sulfite, desiccated Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter,

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and -1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A), said fogged internal latent image silver halide g-ra-ins (11) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (1) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B).

4. A photographic element comprising a support having a first discrete gelatino-silver halide emulsion layer containing unfogged surface image silver halide grains (I) and contiguous thereto a second discrete gelatino-silver halide emulsion layer containing fogged internal image silver halide grains (II) positioned between said first discrete gelatino-silver halide emulsion layer and said support, said silver halide being selected from the group containing of silver chloride, silver bromide and silver chlorobromide, said unfogged surface image silver halide grains (I) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Grams A. N-rnethyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium :brornide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above 1 Z fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate Water to make 1 liter,

said unfogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a mixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes .at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A), said fogged internal latent image silver halide grains (II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (1) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B), the molar ratio of said unfogged surface image silver halide grains (1) to said fogged internal image silver halide grains (II) being from about 10/1 to 1/3.

5. A photographic element comprising a support and a gelatino-silver halide emulsion blend containing unfogged surface image silver halide grains (I) and fogged internal image silver holide grains (II), said silver halide being selected from the group consisting of silver chloride, silver bromide and silver chlorobromide, said unfogged surface image silver halide grains (I) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A) Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-aminophenol sulfate 2.0

Sodium sulfite, desiccated 90 Hydroquinone 8.0

Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter,

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A) said fogged internal latent image silver halide grains (II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (I) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B), the molar ratio of said unfogged surface image silver halide grains (I) to said fogged internal image silver halide grains (II) being from about 10/1 to 1/3.

6. A photographic silver halide emulsion containing unfogged surface image silver halide grains (I) and fogged internal image silver halide grains (II), said silver halide being selected from the group consisting of silver chloride, silver bromide and silver chlorobromide, said unfogged surface image silver halide grains (I) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A) Grams A. N-methyl-p-aminophenol sulfate 0.31

Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

I Grams B. N-methyl-p-aminophenol sulfate 2.0

Sodium sulfite, desiccated Hydroquinone 8.0

Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter,

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A), said fogged internal latent image silver halide grains (II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of said unfogged surface latent image silver halide grains (I) at a total coverage of about 540 19 mg. of silver per square foot and processed for minutes in'said developer (B).

7. A photographic gelatino-silver halide emulsion blend containing unfog'ged surface image silver halide grains (1) and fogged internal image silver halide grains (II), said silver halide being selected from the group'consisting of silver chloride, silver bromide and silver chlorobromide, said unfogged surface image silver halide grains (1) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Grams A. N-methyl-p-aminophenol sulfate 0.31

Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to make 1 liter,

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing said unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 Water to make 1 liter,

said fogged internal image silver halide grains (II) being such that a test .portion thereof, when coated as a silver halide emulsion in its un-fogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in said developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in said developer (A), said fogged internal latent image silver halide grains (II) havin a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion conhi) taining 3 moles of said unfogged surface latent image silver halide grains (I) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in said developer (B), the molar ratio of said unfogged surface image silver halide grains (I) to said foggcd internal image silver halide grains (II) being from about 10/ 1 to l/ 3.

8. A photographic gelatino-silver halide emulsion blend as described in claim 7 wherein the silver halide consists of silver bromide.

9. A photographic gela-tino-silver halide emulsion blend as described in claim 7 wherein the silver halide is silver chlorobromide.

10. A :photographic gelatino-silver halide emulsion blend as described in claim 7 wherein the silver halide is silver chloride.

11. The process for developing a photographic element as described in claim 1 which comprises effecting said developing in a photographic aqueous developer composition in which:

( 1) silver bromide has a rate of solubility greater than that in a solution containing 5 grams of potassium bromide and 20 grams of sodium sulfite per liter of said developer composition at 68 F., and

(2) silver bromide has a rate of solubility less than that in a solution containing 35 grams of potassium bromide and 90 grams of sodium sulfite per liter of said developer composition at 68 F., said second mentioned solution being free of other addenda which increase the rate of solution of silver bromide and free of photographic antifoggant addenda.

12. The process for developing a photographic element as described in claim 4 which comprises effecting said developing in a photographic aqueous developer composition comprising about 40 to 90 grams per liter of an alkali metal sulfite and about 5 to 35 grams per liter of an alkali metal bromide.

13. The process for developing a photographic element as described in claim 5 which comprises elfecting said developing in a photographic aqueous developer composition comprising about 20 to 30 grams per liter of an alkali metal sulfite and about 5 to 35 grams per liter of an alkali metal bromide.

References Cited by the Examiner UNITED STATES PATENTS 2,456,956 12/48 Knott et al. 9622 3,008,829 11/61 Clementi et al. 96109 7 FOREIGN PATENTS 8,099 12/43 Great Britain.

NOMAN G. TORCHIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,178,282 April 15, 1965 George-W. Luckey et al.

' It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent shouldvread as corrected below.

Column 16, line 5, after "N-methylp-aminophenol" insert sulfate lines 56 and 57, for "containing" read consisting column 17, line 41, for "holide": readh d column 19, line 53, for "havin" read having Signed and sealed this 14th day of December 1965.

' (SEAL) Altest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND AT LEAST ONE LIGHT-SENTITIVE PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER, SAID SILVER HALIDE BEING SELECTED FROM THE GROUP CONSISTING OF SILVER CHLORIDE, SILVER BROMIDE AND SILVER CHLOROBROMIDE, SAID PHOTOGRAPHIC ELEMENT HAVING UNFOGGED SURFACE IMAGE SILVER HALIDE GRAINS (I) ADJACENT TO FOGGED INTERNAL IMAGE SILVER HALIDE GRAINS (II), SAID UNFOGGED SURFACE IMAGE SILVER HALIDE GRAINS (I) BEING SUCH AS TO CAUSE A TEST PORTION THEREOF, WHEN COATED AS A PHOTOGRAPHIC SILVER HALIDE EMULSION ON A TRANSPARENT SUPPORT AND UPON EXPOSURE TO A LIGHT-INTENSITY SCALE FOR A FIXED TIME BETWEEN .01 AND 1 SECOND AND DEVELOPMENT FOR 6 MINUTES AT 68*F. IN THE FOLLOWING DEVELOPER (A): 